Darwinism is a term for the underlying theory in the ideas of Charles Darwin, particularly concerning evolution and natural selection. Discussions of Darwinism usually focus on evolution by natural selection.

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Darwinism and other -isms

In the United States, the term "Darwinism" is sometimes used by creationists as a somewhat derogatory term for "evolutionary biology". Casting evolution as an "ism" — a doctrine or belief — is used to strengthen calls for "equal time" for other beliefs such as creationism. However, in other countries — such as the United Kingdom — "Darwinism" carries no such derogatory connotations and is freely used by evolutionary scientists. A notable example of a scientist who uses the term in a positive sense is Richard Dawkins.

Darwinism may also refer to a specific strand within evolutionary biology, dealing with the mechanism of natural selection, which Darwin studied, as opposed to evolutionary processes that were unknown in Darwin's day, such as genetic drift and gene flow. It may also refer specifically to the role of Charles Darwin as opposed to others in the history of evolutionary thought — particularly contrasting Darwin's results with those of earlier theories such as Lamarckism or later ones such as the modern synthesis.

Classical Darwinism

In the 19th-century context in which Darwin's Origin of Species was first received, "Darwinism" came to stand for an entire range of evolutionary (and often revolutionary) philosophies about both biology and society. One of the more prominent approaches was that summed in the phrase "survival of the fittest" by the philosopher Herbert Spencer, which was later taken to be emblematic of Darwinism even though Spencer's own understanding of evolution was more Lamarckian than Darwinian, and predated the publication of Darwin's theory. What we now call "Social Darwinism" was, in its day, synonymous with "Darwinism" — the application of Darwinian principles of "struggle" to society, usually in support of anti-philanthropic political agendas. Another interpretation, one notably favored by Darwin's cousin Francis Galton, was that Darwinism implied that because natural selection was apparently no longer working on "civilized" people it was possible for "inferior" strains of people (who would normally be filtered out of the gene pool) to overwhelm the "superior" strains, and corrective measures would have to be undertaken — the foundation of eugenics.

In Darwin's day there was no rigid definition of the term "Darwinism", and it was used by opponents and proponents of Darwin's biological theory alike to mean whatever they wanted it to in a larger context. The ideas had international influence, and Ernst Haeckel developed what was known as Darwinismus in Germany; though it should be noted that, like Spencer, Haeckel's "Darwinism" had only a rough resemblance to the theory of Charles Darwin, and was not centered around natural selection at all.

Darwinism as selectionism

To distinguish themselves from the very loose meaning of "Darwinism" prevalent in the 19th century, those who advocated evolution by natural selection after the death of Darwin became known as neo-Darwinists. August Weismann was the most prominent member of this school, and further articulated that neo-Darwinism referred to evolution specifically by forms of "selection" (natural selection, including sexual selection), and that it was articulated around the idea that the hereditary material of an organism was not modified by the further development of the organism. Neo-Darwinism poised itself against neo-Lamarckism, also popular at the end of the 19th century and beginning of the 20th century, which argued that bodily modifications acquired during the lifetime of the organism could be hereditarily passed on to the next generation. Weismann's neo-Darwinism, on the other hand, argued that all of an organism's hereditary material was kept in its germ plasm, which existed separately from the rest of the organism's development.

Neo-Darwinism was not terribly popular in the scientific community, as most biologists felt that the complete segregation of development and heredity actions seems unlikely or unwarranted. After the development of the modern evolutionary synthesis in the 1930s, however, the selection theory became increasingly popular amongst biologists, and codified the more modern definition of Darwinism which we have today.

Darwinian processes

In a modern definition of the term, a Darwinian process requires the following schema:

Self-replication/Inheritance: Some number of entities must be capable of producing copies of themselves, and those copies must also be capable of reproduction. The new copies must inherit the traits of old ones. Sometimes the different variations are recombined in sexual reproduction.

Variation: There must be a range of different traits in the population of entities, and there must be a mechanism for introducing new variations into the population.

Selection: Inherited traits must somehow affect the ability of the entities to reproduce themselves, either by survival, or natural selection, or by ability to produce offspring by finding partners, or sexual selection.

If the entity or organism survives to reproduce, the process restarts. Sometimes, in stricter formulations, it is required that variation and selection act on different entities, variation on the replicator (genotype) and selection on the interactor (phenotype).

Darwinism asserts that any system given these conditions, by whatever means, evolution is likely to occur. That is, over time, the entities will accumulate complex traits that favor their reproduction. This is called Universal Darwinism, a term coined by Richard Dawkins in his 1976 book Selfish Gene.

Most obviously, this can refer to biological evolution. However, it has other potential spheres, the best known of which is the meme, a concept of inheritance and modification of ideas introduced by Richard Dawkins in his 1976 book The Selfish Gene and further refined by researchers such as Richard Brodie and Susan Blackmore. It has been disputed if this was a Darwinian process, since it is unproven that memes undergo random mutations.

Perhaps surprisingly Darwinian theories have been proposed as explanations of the origin of the universe we live in. Lee Smolin's theory Cosmological natural selection explains the selection of a universe with the correct fundamental physical parameters to support complex matter such as stars and ourselves. Wojciech Zurek's theory of Quantum darwinism explains the selection of the our classical macroscopic world from underlying quantum processes.

Another example to illustrate are computer systems (PCs). Taking the software as the replicator and the whole system as the interactor, it could be seen as a Darwinian system, however, the code does not change randomly, but is directionally changed or rewritten from scratch; also systems do not reproduce.